Cellulose is one of the most widely utilized polymeric materials. Both unmodified ("native") and chemically modified or derivatized celluloses are of great commercial importance in areas such as textiles, food additives, coatings, filter media, packaging, and medical devices. A recent review of cellulose production and utilization is given in J. Kennedy, G. Phillips, and P. Williams, eds., "Wood and Cellulosics: Industrial Utilization, Biotechnology, Structure, and Properties," Halsted Press, New York, 1987.
Cellulose is obtained principally from the cell wall tissues of higher plants such as cotton, flax, ramie, and both hardwood and softwood trees. It has in recent years become possible, however, to obtain pure celluloses produced by various microbial organisms. Several articles and patents address the special properties and utility of cellulose obtained from microbes:
S. Tamanaka, "Production and Application of Bacterial Cellulose," in Cellulosics Utilization: Research and Rewards in Cellulosics, ed. Inagaki and Phillips, Elsevier Applied Science, 1989. PA1 D. White and M. Brown, Jr., "Prospects for the Commercialization of the Biosynthesis of Microbial Cellulose," in C. Sucherch, ed., Cellulose and Wood Chemistry and Technology, Wiley, New York, 1989. PA1 D. Ring, W. Nashed, and T. Dow, U.S. Pat. No. 4,788,146 (1988), "Liquid Loaded Pad for Medical Applications." PA1 R. Brown, Jr., "Bacterial Cellulose," in J. Kennedy, G. Phillips, and P. Williams, eds., Cellulose: Structural and Functional Aspects, Halsted Press, New York, 1989. PA1 R. Brown, Jr., U.S. Pat. No. 4,942,128 (1990), "Microbial Cellulose Modified During Synthesis", incorporated herein by reference.
In the field of utilization of celluloses, it is well known that the molecular weight of the cellulose or cellulose derivative is of crucial importance in controlling the physical properties of the polymer. There is often a desirable gain in ease of formulation, application, or preparation of cellulose derivatives with a decrease in the molecular weight of the starting cellulose which correlates to a lower viscosity for the resulting cellulose derivative. This is discussed by P. Doty and H. Spurlin on pp 1133 ff. in Cellulose and Cellulose Derivatives, ed. E. Ott, H. Spurlin, and M. Grafflin, Interscience, New York, 1955. Thus, there is a need for producing cellulose with lower molecular weight.
It is known that cellulose can be produced through culture of organisms in the genera Acetobacter, Agrobacterium, Rhizobium, Pseudomonas, and Sarcina. Details of the specific organisms are given in Critical Reviews in Microbiology, Vol. 17, p 436 (1991). Furthermore, certain algal species such as Valonia are known to produce harvestable cellulose.
The most frequently studied bacterial cellulose-producer is Acetobacter xylinum. Articles by Yamanaka, by Brown, Jr., and by White and Brown, Jr., cited above provide reviews of the current status of Acetobacter cellulose production and utilization. Further, S. Kuga, N. Mutoh, A. Isogai, M. Usuda, and R. Brown, Jr. in J. Kennedy, G. Phillips, and P. Williams, eds., Cellulose: Structural and Functional Aspects, Halsted Press, New York, 1989, discuss the determination of the molecular weight of microbial celluloses.
While many workers have reported production and utilization of Acetobacter cellulose, none have reported the existence of a method for the control of the molecular weight of the cellulose produced by the organism. U.S. Pat. No. 4,942,128 teaches that the cellulose produced by Acetobacter grown in a medium containing the additive carboxymethylcellulose possesses an elastic, resilient texture not seen in normal Acetobacter cellulose. Further, Haigler, Brown, Jr., and Benziman report (Science 210, 903 (1980)) that the fluorescent brightener CALCOFLUOUR White ST, when added to an Acetobacter xylinum culture, leads to the production of a cellulose pellicle of modified crystallinity. But these reports all deal with the formation of a cellulose having modified morphology or solid-state properties; none teach the use of culture medium additives to control the molecular weight of bacterial cellulose.
Finally, Ogawa and Tokura (Carbohydrate Polymers 19, 171 (1992)) report that when grown in a medium containing N-acetylglucosamine, Acetobacter xylinum produced a cellulose pellicle containing from 0.5-4.0 mole % N-acetylglucosamine incorporated into the cellulose chain. They do not report or discuss the molecular weight of the polymer produced by this procedure.
The present invention as described below, provides a novel method for producing microbial celluloses having molecular weights different from that of normal, "unmodified" microbial celluloses.